/*
 * ice4j, the OpenSource Java Solution for NAT and Firewall Traversal.
 *
 * Copyright @ 2015 Atlassian Pty Ltd
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.ice4j.attribute;

import org.ice4j.*;

/**
 * This class implements the USE-CANDIDATE attribute This attribute is an
 * extension to the original STUN protocol This is used only during an ICE
 * implementation
 *
 * This attribute serves as only a flag, it does not have any data so the data
 * length is zero
 */
public class UseCandidateAttribute extends Attribute {
	/**
	 * Data length.
	 */
	private static final char DATA_LENGTH_USE_CANDIDATE = 0;

	/**
	 * Constructor.
	 */
	protected UseCandidateAttribute() {
		super(USE_CANDIDATE);
	}

	/**
	 * Decodes the USE-CANDIDATE attribute's body, which is empty
	 *
	 * @param attributeValue
	 *            a binary array containing this attribute's field values and
	 *            NOT containing the attribute header.
	 * @param offset
	 *            the position where attribute values begin (most often offset
	 *            is equal to the index of the first byte after length)
	 * @param length
	 *            the length of the binary array.
	 * @throws StunException
	 *             if attrubteValue contains invalid data.
	 */
	void decodeAttributeBody(byte[] attributeValue, char offset, char length) throws StunException {
		// Do nothing, empty attribute body
	}

	/**
	 * Returns a binary representation of this attribute.
	 *
	 * @return a binary representation of this attribute.
	 */
	public byte[] encode() {
		char type = getAttributeType();
		byte[] binValue = new byte[HEADER_LENGTH + DATA_LENGTH_USE_CANDIDATE];

		// Type
		binValue[0] = (byte) (type >> 8);
		binValue[1] = (byte) (type & 0x00FF);

		// Length
		binValue[2] = (byte) (DATA_LENGTH_USE_CANDIDATE >> 8);
		binValue[3] = (byte) (DATA_LENGTH_USE_CANDIDATE & 0x00FF);

		return binValue;
	}

	/**
	 * Compares two STUN Attributes. Two attributes are considered equal when
	 * they have the same type, length and value.
	 *
	 * @param obj
	 *            the object to compare this attribute with.
	 * @return true if the attributes are equal and false otherwise.
	 */
	public boolean equals(Object obj) {
		if (!(obj instanceof UseCandidateAttribute))
			return false;

		if (obj == this)
			return true;

		UseCandidateAttribute useCandidateAtt = (UseCandidateAttribute) obj;
		if (useCandidateAtt.getAttributeType() != getAttributeType()
				|| useCandidateAtt.getDataLength() != getDataLength())
			return false;

		return true;
	}

	/**
	 * Returns the length of this attribute's body.
	 *
	 * @return the length of this attribute's value.
	 */
	public char getDataLength() {
		return DATA_LENGTH_USE_CANDIDATE;
	}

	/**
	 * Returns the human readable name of this attribute.
	 *
	 * @return this attribute's name.
	 */
	public String getName() {
		return "USE-CANDIDATE";
	}
}
